Transmission system



Nov. `16 1926.

E. L. NELSON TRANSMISSION SYSTEM Filed August 5, 1923 2 Sheets-Sheet 1 Filed .August 5, 1923 2 Sheets-Sheet 2 *1 760.0150 +A veaooomzsz CJI Patented Nov. i6, 1926.

NETE@ STATES EDVARD L. NELSON, QE' EAST ORANGE, NEVI J, SSG- 'ER-IC COMSANY, INCORPORATED, 0E NE?? YORK, l. Y., l

YORK.

OR T0 WESTERN ELEC- CORRATION OT? NEW' TRANSMISSION SYSTEM.

Application filed August 3, 1923.

This inventionL relates to transmission systems and more particularly to systems for radio transmission for duplex ship-to-shore communication over considerable distances.Y

in object of the inif'ention is to provide a system for duplex radio transmission employing highly selective and eiiicient receiving apparatus of such a type as to avoid the necessity for synchronizing high radio frequencies. in radio telephone transmission Where-in carrier frequencies of 500,000 cycles per second and upward are employed and wherein the uninodulated carrier component is suppressed at the transmitter in accordance With methods Well known at the presenttime, dihiculties have been encountered in connection with keeping the carrier frequencies correctly synchronized or correctly spaced apart. it is a particular object of this invention to avoid the necessity for synchronization of such high car ier frequencies. In order to accomplish this desired result. the present system .is so arranged that only some reaitively row frequency sources such as from about 8.000 to 90,000 cycles per second need be synchronized.

n. further object is to provide a system of transmission such that although high frequency balanced modulators are employed no enact or perfect balance is required.

still further object is to provide a systeni in which the full advantages of suppression of the unmodulated carrier component are obtained Without the disadvantages of synchronizing high radio frequencies or transmitting synchronizing energy from one station to another.

i further object is to prevent high or other frequency singing` at a radio terminal or radio repeating station in which the frequency of the outgoing energy is controlled by received incoming energy. n

in one organization of `parts for carrying into effect the principles of theV invention, the ship station consists of a transmitter of almost any simple 1sind and a receiver of the double detection type. The transmitter and the receiver are connected to the saine aerial structure. A loop resonant circuit is connected in the receiving branch in order to reduce to a small amount the energy of the transmitting` Wave length traversing this branch. The portion of the outgoing carrier frequency Wave which is unsuppressed Serial No. 655,395.

by this tuned circuit combines With the incoming Waves to step them down to an intermediate frequency as a result of the rst detection. A carefully stabilized oscillator operating at the intermediate carrier frequency supplies an unmodulated component of sufficient energy. For reasons which Will be stated hereinafter, the intermediate frequency Will remain constant, hence the oscillator, which supplies 'current of this frequency may be left fixed after being once adjusted. As will be observed from the foregoing description the ship station is of a simple type.

The shore station will novv be described. An oscillator supplies Waves of a base frequency of 10,000 cycles per second. These oscillations are modulated by the message Waves to be transmitted, in a balanced modulation circuit which suppresses t-he unmodulated component. A band filter selects one resultant side band which is transmitted to the input circuit of a second balanced modulator. rEhe second balanced modulator is supplied With oscillations of aV frequency of 50,000 cycles which are produced from the .source of 10,000 cycles frequency by means of a harmonic producer, a selective circuit to select the fifth harmonic, and an amplifier. rlhe output of the second modulator consists of tivo side bands one having 40,000 cycles and the other having 60,000 cycles as the carrier frequency. One of these side bands for example the latter, is selected by a band filter and supplied-to a third balanced modulator circuit to Which is also supplied a Wave having the exact frequency of that transmitted from the kship station. In order to secure this, the Wave energy from the ship station is received in an auxiliary receiving relay and passed through a suitable series of selective circuits and ample fiers. If the carrier frequency transmitted from the ship station is 760,000 cycles, this is combined in the balanced modulator circuit With the modulated side band based upon a carrier of 60,000 cycles to produce new side bands, one of which Will be based upon a carrier of l?00,000 cycles per second. This Wave is amplified in the power amplifier circuit and radiated to the ship station. The carrier Wave radiated from the ship station may have a certain allowable frequency variationv of the .order of some Y ate or beat frequency resulting from the combination of these two carriers will be constant.

Since the unmodulated component of carrier frequency is entirely or largely suppressed, it is necessary to supply this coinponent before the final stage of detection. Inasmuch as the intermediate frequency is constant and is low, relative to the principal carrier frequencies, the problem of synchronization is reduced to one of synchronizing within the required'limit, a source of oscillations of the order of 8,000 to 90,000 cycles per second rather than carrier oscillations of the order of 500,000 to 1,000,000 or more cycles per second.

The novel features which are believed to be characteristic of the invention are set forth in their particularity in the appended claims. The invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof will best be understood by reference to the following detailed description, taken in connection with the accompanying drawing in which Fig. 1 shows diagrammatically the circuit arrangement employed at a shore station; Fig. 1a is a modification, illustrating the adaptationA of the circuit of Fig. `1 for a radio repeater; Fig. 1b is a modification illustrating a simplified form of the circuit of Fig. 1; and Fig. 2 is a circuit diagram of a form of circuit which may be employed at a ship station. l

In Fig. 1, microphone 1 indicates a telephone line or other source of outgoing messages designated by the frequency s1. These Waves are applied to the input circuit of a balanced modulator 2 of the type described on pages 308 and 314e of a paper by Colpitts andV Blackwell, entitled Carrier current telegraphy and telephony inyolume 4-0 of the Proceedings of the.` A. I. E. E. A source 3 consists of a vacuum tube generator or other device for producing waves of a base frequency of 10,000v cycles per second. Various means are known for causingsuch a relatively low frequency ,generator to be very constant injfrequency and the employment of such arrangements as are necessary to maintain the frequency very constant is contemplated.

One of the two side bands produced by the balanced modulator 2 is selected by the band filter fl and impressed upon a second balanced modulator 5. The balanced modulatcr 5 is supplied also with waves of the constant frequency of 50,000 cycles produced by impressing waves from the source 3 upon a harmonic producer 6, selecting the fifth harmonic in a selective circuit or seri-es of selective circuits 7, and amplifying the selected 50,000 cycle component in an amplifier 8.

rl'he balanced modulator 5 produces in its output circuit two speech side bands, one based upon a frequency of 410,000 cycles and the other upon a frequency of 60,000 cycles. The 00,000 cycle side band is selected by a band lter 9 and supplied to a balanced modulator 10.

Each band filter in the present system is a structure for passing a band of frequencies and excludingi other frequencies and may be constructed in accorcance with the theory set forth in Patent No. 1,227,113 granted May 22, 101'? to G. A. Campbell. However, it is contemplated that under certain conditions other selective means may be employed in place of band filters, the only requirement being that some arrangement is used which will produce the desired degree of selectivity. Such arrangements as thus described by iler-:anderson in Patent No. 1,173,079 February 22, 1916 may be employed.

The balanced modulator 10 is supplied with wares the carrier 'frequency radiated from the ceoperatinpr ship station. These are produced by receivingv the carrier wave rom the ship in an auxiliary antenna 11, se- .ecting the unmodulated component ina cries of sharply tuned selective circuits 12, ind amplifying' the energy selected in an amplifier 13 of any suitable type. it is not ecesscfy that the circuits 12 discriminate completely accompanlv y side band or bands but some discrimination is desirable.

In thc output circuit of the balanced modulator 10 will be produced two speech side bands, one based upon the carrier frequency of 820,000 cycles and the other upon the carrier frequency of 7 00,000 cycles per second. The lower of these, namely 7 00,000 cycles, is selected by the ban d filter 14:, amplified bythe power amplifier 15 and radiated from the transmitting antenna 10.

lt is assumed that ship station is sendon a carrier frequency of 700,000 cycles per second and is radiating some enercy of this frequency during' r ception periods on the ship. Therefore,- if the ship station be of the carrier suppression type which is not an essential feature of this system it must not suppress the carrier to such an extent that the shore station will not be able to piclr up an appreciable amount of energy in the auiliary receiving' antei na 11,

l'n accordance with the present invention, it is contemplated that the carrier ware radiated from the ship need not be exactly fixed, it may vary by some indeterminate amount which we may designate as A., A representing a frequency variation from 0 to some hundreds of cycles or possibly more,

between the incomingcarrier and y Cil and being either a ositive or negative quan- 1 Therefore, on the drawing, symbol A represents the possible Variation of the carrier frequency of the ship station which may hare anyv Value from Zero up to some liundreds of cycles per second. inasmuch a ce carrier frequency radiated from the ore Station is always the same as that of e 'L minus exactly 00,000 cycles e intermediate or b ,at frequency produce'L each station by the combination of these o will be fixed and invariable so long' as the 10,000 cycle generator 8 at the shore stati renains fined and invariable.

ln orde to adapt the arrangement of Fig. o operate as a repeater str ion. the appaus to the left of the line i-X in Fig. 1 may he replaced by a gene of oscilla- `ois of the frequency of 00,000 cycles as lustrated by 11. ln thus adapting' the. sj/,fstein te function as repeater station the selec-tire circuits 12 and the amplifier 13 should be modified to pass not only the can rier frequency incoming to the antenna 11 but also the signal carrying; side band accompanying this carrier frequency. rlhe Wares radiated from the antenna 15 Willl differ from those received by the antenna 11 in haring their frequency changed by the lined amount ef 00.000 cycles and their energy greatly amplified.

In 1J is illustrated a simplified form of the circuit arrangement of Fin'. 1. rthe balanced modulator 2, the band filter el, the harmonic reproducer 07 selective circuits 11, and the amplifier S are eliminated.

Carrier 'Wares of the frequency of 00,000 cycles are provided from the source 17 to a balanced modulator 5 along' with the signal Waves from the microphone circuit 1. rlhe band filter 0 selects one side band and impresses it upon the balanced modulator 10. rlhe operation of the remaining' parts of the system is identical with that described in connection With 1. ln this simplified in, the carrier frequency of 00,000 cycles maintained constant mi nin the i f es u c t maintained exactly coista*- in frequeicu. plifying apparatus for produc nio ted hi gli frequency i of the necessary -ioWer are indicated by th i 1 ...i 1 Tne modulating a 20 maf.7 be such as to radizite a single ing` side band accompanied either` b normal amount or by a relatively s ill amount of unmodulated carrier component. Suppression of the unmodula c carrier component is not essential and both side bands may be radiated if desired. In order to fulfill the condition of the greatest possible simplicity of th-e ship circuit this arrangement is preferred. A simple transmitter such as described by Helsing in the Proceedings of the .institute of Radio Engin ers for August, 19217 page 3&2, may be employed.

branch 21 is extended from the ship antenna for the purpose of receiving.V 1n this branch is a tuned loop resonant circuit 22 which is designeeL to off-er avery high irnpedance to the outgoing` carrier and the accompanying side band or side bands. Tuin ing` elements 23 serre to give the antenna one natural frequency of resonance at or nea-r the frequency of the incoming Waves Which are thus impressed upon the detector D1 after being selected inthe selective circuit 211. The detector D1 steps. down the frequency of the incoming Waves by combining them with the energy of the outgoing carrier Waves so as to produce in the tuned circuit 25, a combination frequency.

ln order to reproduce a signal of goed quality7 it is necessary to supply7 an unmodulated carrier component for further detection. This is done by means of the Vacuum tube or other generator Q6 which is carefully adjusted to the desired intermediate frequency carrier which, in the present instance, is 60,000 cycles per second.

ln general, the source 26 may consist of a carefully shielded vacuum tube oscillation generator constructed in accordance with Wn principles whereby the frequency may be lreptquite constant. The Wav-esfrom the source 20 are supplied to the tuned circuit 25 and impressed upon the det ctor D2. rlelephone receivers 27 are connected to the out put circuit of the detector D for receiving the signal.

The receiving apparatus at the shore station has not been illustrated in Fig. 1. Any suitable type of receiving system may be employed. A receiving system such as shown in Fig. 2 may be coupled directly to the antenna. 11. The tuned circuit 2e is coupled loosely to a coil in the antenna 11. To the left of the line Y-Y will be plc-.ced the paratus indicated as being` to the left of the line Y-Y in Fig. 2. il loop or other antenna tuned to the incoming carrier frequency may be used as a signal receiving, antenna in place of the antenna 11. This loop may be located a small or great distance from t ie antenne 11 and 16 as may be convenient or desirable. instead of the. source Q6, the sixth harmonic produced by the harmonic producer 6 may be selected by means of suitable selecting circuit and applied to the input circuit of the detector D2 of the shore terminal receiving` circuit.

Among the advantageous operating features of the system herein described are:

1. Suppression of the carrier and one side Y the cost.

8. Highly accurate control of the carrier frequency on the ship station shown in lflig. 2 is unnecessary.

il. The problem of carrier synchronization is reduced to that of maintaining,` 10,000 or 60,000 cycle sources within the required limits.

` 5. The circuit of the shore station shown in Fig. 1 will not sing` because current wave@ of the frequency sent out by the antenna 16 are tejreatly attenuated by the antenna 11, selective circuits 12, balanced modulator 10 and band filter 111. Any current of the frcquency received in the antenna 11 d oes not produce sufficient energy of the outgoing` carrier frequency in the antenna 16 to cause singing. Consequently, relatively large ampliications in the amplifiers 18 and 15 may be secured.

6. Relatively imperfect carrier suppression in the balanced modulators 2, 5 and 10 is permissible as the band iilters fi, 9 and 11i aid in suppressing the carrier.

The novel features believed to be inherent in the invention are set forth in the appended claims.

llfhat is claimed is:

1. llhe method of signal transmission between two stations by means of carrier vaves of different frequencies which coniprises allowingthe frequencies of the car-V rier waves to vary but inaintainingl their difference constant.

2. yShe method of transmission between two stations by means of carrier waves which comprises allowing the frequencies of the carrier waves to vary but maintaining` their difference constant, and supplying at onestation a wave of the constant difference frequency.

3. The method ofsignal transmission between two stations by means of carrier Waves which comprises allowing,- the frequencies of the carrier waves to vary but maintaining their difference constant, and supplying a wave of the constant difference frequency at both stat-ions.

e. 'T he method of signal transmission between two saations by means of carrier waves which comprises allowing the fr quencies of the carrier waves to vary but y.

maint ining,- their difference constant, cornbining the carrier waves at one station to produce a Vdifference frequency, and supplying; an unmodulated component of the constant dilference frequency atsaid station. 5. rllhe method of signal transmission between two stations by means of carrier waves which comprises allowing the frequencies of the carrier waves to vary but maintaining i'i' difference constant, combining the car- :es at each station to produce a difference frequency wave, and supplying an uninodulated component of the constant diff isequency at each station.

(i. 1^ n a angement for signaling between sca-.tion and a movable station by i relatively simple apparatus at the tion in combination with apie fixed station which comprises receiving circuit, a supplemental ier receiving carrier waves from a `ition, means for producing a rratively constant frequency wave fixer. station, and means for come'aid wave with said `received carrier s to produce an or-.tgoingcarrier wave `ie diiiering from the received l kL . wave by a fixed and determined irreipcctive of frequency variations requency of the received wave. i a radio transmission system for twocommunication betweenv a' station, siniplicity of apparatus is the chief deratum, and another station which compri is at the first named station a trans` 'sting circuit of any desired kind including means for producing,` a carrier wave, and lying circuit comprising),l a detecting producing a combination frency wave, oscillation generator for a wave to combine with the comequency wave, and a detector for vin@i the combined wave; and at the er station a receiving circuit for receivthe wave transmitted from the iii-st 'v 1)' C3 i, `ined station, means for producing` a rela-- tively .low frequency carrier wave modulated accordance with a signal to be transl. means for combining the modulated iv with the received wave to produce a inodiidaed difference frequency wave which from the received wave by a constant diners amount, and means for radiating the moduted difference frequency wave.

il. The method of maintaining,` thedifference between incoming` and outgoing' cari waves constant in a carrier wave terl station having an inherently varying outgoing carrier wave source, which comprises receinigl the varying wave at a disstation, and sending back from said at u a carrierV wave differing therefrom etant aniount.

Y ss whereof, i hereunto subscribe my name this dav of July A. D., 1923.

nnvvann n. unison. 

